How should I update a textbox value in a WPF app? - wpf

Question

I'm troubling to resolve how a textbox should automatically change its value when a object is updated. I have a Temperature class with Name and Value.
public class Temperature
{
public string Name { get; set; }
public double Value { get; set; }
}
In MainWindow.xaml.cs after InitializeComponent(), I create an
ObservableCollection _lstTempObs = new ObservableCollection(); and then I add an initial temperature object.
In the main window I have a textbox
<TextBox x:Name="T1" Text="{Binding Path=Value}" HorizontalAlignment="Left" Height="23" Margin="215,55,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
And in MainWindow.xaml.cs I set the datacontext as
T1.DataContext = _lstTempObs.LastOrDefault();
The temperature update comes from an API. When I get the mew Temperature object, I add it in the ObservableCollection, but the value isn't change in the GUI.
public partial class MainWindow : Window
{
ObservableCollection<Temperature> _lstTempObs = new ObservableCollection<Temperature>();
public MainWindow()
{
InitializeComponent();
_lstTempObs.Add(new Temperature { Name = "T1", Value = "0.321" });
T1.DataContext = _lstTempObs.LastOrDefault();
}
}

Answer 1

you need to implement a notification-mechanism that informs the UI of changes to the data.
In WPF this is usually done using INotifyPropertyChanged-interface.
Check this answer for a basic reference on how to do that.
In a actual scenario I would implement the INPC-interface in a base class
public class INPCBase : INotifyPropertyChanged
{
public bool SetField<U>(ref U field, U value, [CallerMemberName] string propertyName = null)
{
if (field == value))
{
return false;
}
field = value;
OnPropertyChanged(propertyName);
return true;
}
public event PropertyChangedEventHandler PropertyChanged;
public virtual void OnPropertyChanged([CallerMemberName]string propertyName = "")
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs(propertyName);
handler(this, e);
}
}
}
Usage:
public class Temperature : INPCBase
{
private string name;
public string Name { get; set{base.SetField(ref name, value); } }
private double val;
public double Value { get; set{base.SetField(ref val, value); } }
}